Refining mineral oils



Jan. 25, 1944. R. F. PFENNIG ETAL REFINING MINERAL OILS Filed April 26, 1940 mww OIR YW; Ok.

Patented Jan. 25, 1944 REFININ G MINERAL OILS Reuben F. Pfennig and Claude R. Davis, Baytown, Tex., assignors to Standard Oil Development Company, a corporation of Delaware Application April 26, 1940, Serial No. 331,698

2 Claims. (Cl. 196-41) The present invention relates to the refining of mineral oils. The invention especially relates L to the refining of petroleum oils for the production of high quality lubricating oil distillates. In accordance with the present process, petroleum oils, particularly those petroleum oils boiling in the lubricating oil range, are contacted in an initial stage with an anhydrous molten alkali It is known in the art to refine crude petroleum l oils by various procedures in order to produce satisfactory products. For example, in the processing of lubricating oil stocks derived from naphthenic crudes, it is known that certain constituents, such as naphthenic acids and the like, must be removed for the production of neutral distillates. A usual procedure for accomplishing this result is to inject aqueous solutions of sodium hydroxide orY equivalent solutions directly into the still, preheater, or fractionating tower and to allow the distillation to proceed in the presence of this alkali. Various modifications of this process are also employed, one of which is to inject dry lime into the preheater or stilll in order to neutralize acidic compounds .which results in an improvement in the color of the refined oil. It is alsov known to pass mixtures of petroleum vapors and steam through a strong aqueous alkali solution or through a fused body of sodium hydroxide at elevated temperatures. Another practice is to contact petroleum vapors with fused caustic in a distillation tower by circulating the liquid caustic over several plates near the bottom of the tower. By operating in this manner, the vapors from the still are passed countercurrently through the liquid caustic, thus neutralizing acidic materials and eecting a color improvement in the distillate. Hydrocarbon oils have also been extracted with aqueous solutions 'of sodium hydroxide at relatively high temperajtures, for example, in the range from about `300 F. to 400 F. and at elevated pressures such tends to cause deposition of the caustic (intheA wall of the equipment'and heating means, which materially decreases heat transfer rates and increases operating costs. Furthermore, it is necessary to frequently clean the equipment, thus substantially decreasing its yearly throughput. Other disadvantages encountered in current f .i processes are the extensive pressure drops which are incurred, particularly in vacuum distillation operations, as well as the formation of emulsions which are difficult to break.

We have now discovered an improved process for the production of high yields of improved quality products which have a better color and color stability thanv has heretofore been secured by known processes, which comprises an initial stage in which the feed oil is first contacted with a fused alkali and a secondary stage in which the treated oil is distilled under controlled conditions. Our process produces oils which finish to a low neutralization value yand which have exceptionally good cast and high color stability.

In accordance with our process, the feed stock is contacted in the liquid phase at approximately atmospheric pressure with an anhydrous caustic molten alkali which may or may not be mixed with another anhydrous material capable of lowering its fusion point, but which does not change its chemical activity. After contact of the feed stock in an initial stage, the oil is distilled in a secondary stage under controlled conditions to secure the desired products.

The process of our invention may be readily understood by reference to the attached drawing illustrating modifications of the same. Crude oil, which for the purpose of the description is taken to be a naphthenic` crude, is withdrawn from crude storage tank I and introduced into furnace 2 by means of liney 3 and pump 4. The oil is heated in furnace 2 and then introduced into distillation tower 5 by means of line 6. Temperature and pressure conditions are regulated on distillation tower 5 adapted' to remove overhead by means of line 1 hydrocarbon constituents boiling in the motorV fuel, kerosene, and gas oil boiling ranges. It is to be'understood that distillation tower 5 may comprise any number of units arranged in any desirable manner. The residual oil substantially free of hydrocarbon constituents boiling in the motor fuel, kerosene, nand gas -oil boiling ranges is withdrawn from ldistillation towerAS'by means of line 8 and pump '.9' 'Elie residuunisinen mixed with a fused alkali which is introduced by means of line lil and the mixture introduced into mixer II. For purposes of description, the fused alkali is taken to be an anhydrous mixture of sodium hydroxide and sodium carbonate. The mixture comprising residual oil, fused sodium hydroxide, and sodium carbonate is withdrawn from mixer II by means of line I2 and introduced into settling zone I3. Settling zone I3 is so designed that the residual oil is in contact with the fused alkali for an optimum time period at thedesired temperatures." The desired temperature in settling zone I3 is maintained by heating means 'I4 comprising lines I5 and I5. The fused alkali mixture Other desirable alkali mixtures comprise sodium hydroxide admixed with various anhydrous inorganic salts which are capable of lowering the fusion point of the sodium hydroxide. Particularly desirable salts are sodium carbonate, sodium sulde, sodium bromide, sodium iodide and sodium sulfate. An especially desirable alkali mixture utilizing sodium hydroxide comprises a mixture of sodium hydroxide and anhydrous sodium carbonate. When employing this mixture, it is desirable to use at least 75% sodium hydroxide, preferably from 85% to 95% sodium hydroxide. A particularly desirable mixture comprises 92% sodium hydroxide and 8% sodium caris withdrawn from settling drum I3 by means 1'5"bonate. The alkali should be substantially anof line Il and recycled to the mixer as described hydrousg In no instance is it desirable that the by means of recycle piunp I8. Spent fused alkali moisture content of the treating alkali or alkali may be Withdrawn from the system by means of mixture exceed about 2.0%. In general, the line I9, while fresh or make-up aikali Amay 4be moisture 4content of the alkali treating agent introduced from make-up alkali drum 'by 20 should'be below about 0.5% and should prefermeans of pump 2I and line 22.. The d-esiredtem'- rably be anhydrous. perature is maintained in make-up drum 20 by The time of contact between the fused anmeans of heating coil 23 which comprises lines hydrous alkali mixture and the oil will depend 24 and 25, The alkali contacted oil is withdrawn upon the .feed oil ,being treated, the particular from .settling zone I3 by meansofline 26., passed 25 alkali oralkali mixture employed, aswell as through furnace 2'I and introduced into distillauponthe, temperature atwhich the` oil istreated. tion tower 28.. Temperature and pressure condi- For example, when treating .a feed oil derived tions of distillation tower 28 are adapted to refrom a n aphthenic 'crude and which boils inthe move overhead by means of line 29 the desired range aboveabout50n? F., itis preferredtoconproducts and to remove by means o! line 3.0 a 30 tact the l.Same for va period 0f from-5 to-25minresidue. It `is to be understood that distillation utes, preferably from 10 tov20 minutes, at a suittower 2.8 may comprise any number of towers arable temperature ranging between 370a F. 'and ranged in any desirablemanner and that one or 700 F., preferably fromabout500te F. to ,550 F. more side streams may be segregated. The pressures employed seldom Vshould, exceed The process of the present invention may be 30 one or. two atmospheres and, in general-,the operwidely varied. The invention comprises procation should be conducted at aboutatmospheric essing feed oils .in a two-stage operation, the inipressure. The Quantity Of'anhydlOllS fused alkali tial stage of which comprises contacting the feed used per. volume of oil likewise will vary conoil inthe liquidstate with a fused alkali, folsiderably. VIngeneral, the quantity 0f fused allowed by distilling the alkali contacted oil in a 40 kll Will Valyin the range from about 0.1 volume secondary distillation stage. The process may be 11073 Volumes Of alkali Per Volume 0f Ol- In gen.- adaptedtothe treatment of any feed oil. The eral, it is preferred to employ vfrom 1.0 to 1.5 invention, however, is particularly adapted for the volumesof anhydrous fusedy alkali per volume of processing of oils containing naphthenie bodies, `oil. Theralkali treated oil'after separation from especially for processing lubricating oil stocks the alkali is then heated Vt0 a Alfcrlfllerature .0f derived from naphthenic crudes. In accordance about 6009 F. to 700 F., and discharged preferwith the preferred modification of the present inably into the vacuum distillation equipment,y in vention naphthenic crude oils are distilled at subwhich the respective streams `are segregated from stantially atmospheric pressures underl conditheresidue. tions to remove overhead fractions boiling in the In'order to further illustrate our invention, the motor fuel, keroseneand'gas oil boiling ranges followingoperations are givenwhich should not and to produce a residuum substantially free of be'construed as limiting the sameA in any manner these constituents which is then processed in whatsoever: accordance with the present invention. In gen- -Gperation I.-A coastal crude having a neueral, it is preferred that the ,residuum should tralization `value equivalent to .1.20 milligrams `of have an initial boiling point above 450 F., prefptassium hydroxidev per Vgram of oil Vwas 4diserably in the range above 550 F. tilled under atmospheric pressure ata liquid still Although any anhydrous fused alkali may, untelrilielraturel of A600" F. for theremoval of, the der certain conditions,`be employed, Yweprefer light DrQdllCtS. Such as naphliharkeloseneandas to utilize anhydrous alkali metal hydroxides, Oil- One YQlllme. v0f the resultant. residuumwas such as sodium hydroxide and potassirun hydroxthenintmately,contacted with about 1.5 volumes ide. An especially desirable treating agent comof a Amolten.,causticalkali.reagent consisting of prises a mixtureof sodium hydroxide and potas- 92% vNaOH 'l11' 'f8%v Na2COrby. weight '(fuSiOn sium hydroxide, particularly when the concen- I )OrliV ab01llL510 F.) for labout 10'` minutes .alia trationrof the sodium hydroxide is in the Yrange temperature of .550 F. After settling andsepfrom about 25% to 85%. In general, the most arating the voil fromY the reagent, the`- caustic. satisfactory operation is secured when the so.-

treatedoilwas chargedto a vacuumfstill 'and dium hydroxidepotassium hydroxide mixture distilled .into finished overhead fractionshaving comprises from 45% to 55% of sodium hydroxide. 70 the following properties:

vis. at'F.. s. s..U v88j .100 128.. 240 286 728 823 877 1, 534 c1dr,Tsg-R0binson plus 1x7- 17 17 17 11 11.75 12 -11- 9 Commonnamaazzso"F.),TagRobinson 1a `16.25 15.254 12 12,25V io 10.25vv io i 1.75 Neerslizauqs ys1ue ourl v0.02 dos o..o3 dos, 0,01 `dosI 0.93 0.01

For purposes of comparison, a similarlytopped crude was Vvacuum distilled over 200% of the theoretically required .amountof lcaustic injected into thek still as a 50 Baum aqueous solution. Thefollowing oils were obtained:

Operation IV.-The following :operation illustrates the suitability of a mixture of sodium hydroxide and potassium hydroxide as a molten alkali treating reagent for the production of neutral and relatively color stable lubricating oils Vis. at 100 F., S. S. U 64 Color, lTag-Robinson 17 Colorhold (16 hrs. at 250 F.), Tag obinson 1 Neutralization value 0. 02

' It will be noted from the above that the oils produced in accordance with the usual method of distilling over an excess of caustic require additional chemical and physical treatment to render them color'stable, whereas those produced Viscosity at 100 F., S. S. U 144 1,009 Color Tag-Robinson 17 9.25 Colorhold (16 hrs. at 250 F.), Tag-Robinso 12. 25 6. 5 Neutralization value 0. 014 0.03

A comparison of these data with those presented under Operation I shows that the use of greater amounts of reagent renders the oil more color stable; nevertheless, this relatively small treat with molten alkali produced oils far superior in color stability to those produced by the usual method of distilling over caustic.

Operation III .-A study was made of the eiect treating temperatures and times of contact have on the color and color stability of molten alkali treated oils. Several batch treats were made on a reduced coastal crude employing a molten mixture of alkali consisting of 92% of sodium hydroxide and 8% sodium carbonate as the reagent in each case but with varying temperatures and times of contact. In each of these treats, approximately one volume of oil was intimately contacted with 1.5 volumes of the molten reagent for the predetermined time at the selected temperature. Each of the several batches rof treated reduced crude was then distilled into three overhead cuts and a residuum. The following inspections are typical of those obtained on the lube stocks produced in these operations:

from naphthenic crudes. In these operations, two batches of reduced Coastal crude were intimately contacted with a molten alkali mixture consisting of 51% NaOH and 49% KOH for 10 minutes, employing a contact temperature of 420 F. in one instance and 550 F. in the other. The volume ratio of oil to reagent was approximately 1 to 1.5 in each case. Each of these treated batches of reduced crude was distilled under vacuum to yield lube oils having the following properties: o

Treating temperature Viscosity at 100 F., S. S. U 130 861 132 816 Color, Tag-Robinson 17 11.75 17 13.75 Color-hold (16 hrs. at 250 F.), Tag- Robinson 17 10 16.25 10.75 Neutralization value 0.01 0.03 0.01 0.035

Although in these operations only one particular mixture of sodium hydroxide with potassium hydroxide was employed as the reagent, it is evident that other mixtures can be used equally as well to produce high quality oils so long as the fusion point is not suiiiciently high to cause cracking of the oil.

Operation V.A batch of reduced Coastal crude was contacted with molten sodium hydroxide for 10 minutes at 650 F. The ratio of oil to reagent employed was approximately 1 to 1.5 by volume, respectively. The lube distillates vacuum distilled from this treated reduced crude had the following properties:

Although these oils are relatively color stable, their quality is not quite as good as that of the oils treated at lower temperatures with either a mixture of sodium hydroxide with sodium carbonate or a mixture of sodium hydroxide with potassium hydroxide.

Distillate cut, per cent reduced crude Contact time with Reagent. .-minutes. 10 10 10 10 20 30 Temperature of contact-.. 550 650 650 550 550 550 Viscosity at 100 F., S. S. 125 150 987 877 791 771 Color, Tag-Robinson 17 17 9. 25 11 10. 75 10. 5 Golorhold (16 hrs. at 250 F.), Tag-Robinson 15. 25 10. 75 7. 25 10 9. 25 9. 25

The above data indicate that the lowest treat- Operation VI .-A reduced Panhandle crude was ing temperature and the shortest time of contact available with good mixing gave the best oils although increased time of contact at the lower temperature did not appreciably harm the color stability.

contacted for 10 minutes at 550 F. with a molten caustic alkali consisting of 92% NaOH and 8% NazCOa. The ratio of oil to reagent was approximately 1 to 1.5 by volume, respectively. By vacuum distillation, oils with the following proper- Panhandle crude:

ties were `obtained .from this .treated reduced Viscosity at 100 F., S. S. U i5l 94 Solid Color, Tag-Robinson `19. 25 14.25 9.25 Colorhold (16 hrs. at 250 F.), T.-R 14. 5 1.125 3. 5 Neutralization value 0. 0l 0.007 0.02

By way of comparison, .the above oils had much better color stabilities than `did similar oils prepared from reduced Panhandle crude which had notbeen subjected to any Atreatment other vthan distillation. The following inspections, are representative for suchV untreated oils:

Viscosity at 100 F., S. S..U 42 85 Solid Color Tag-Robinson 20.5 16 8.5 oolorliom (16 hrs. atmen), 'ix-R 11.15 4. 75 0.75 Neutralization value 0. 12 0.14 0.16

Additional tests were conducted for stabilizing the color of cracked oils by molten alkali treatment. Although improvement in their properties was realized, it; was necessary to subject the cracked oils to other chemical treatment, such as sulfuricacid, in .orderto obtain iinished oilsliav- A,ing the .desiredcolor and. color stability.

'The .invention .claimed isz l. Process .for ithe...production .of oils `effimproved color stability and castand low neutralization value from feed oils boiling in the range above about 500 F, and derived from naphthenic crude oils comprising contacting saidfeed oils in the liquid state in an initial stage lat a. tempera- .turev in the range from about .500 F. to about 550 F. and at atmospheric pressure for aperiod of from about 10 minutes to Iabout .20 minutes with an anhydrous fused alkali, separating the treated oil from the fusedl alkali and subjecting the-same to a distillation operation in a secondary stage under conditions adapted to remove high quality products overhead.

2. Process in accordance with, claim 1, in which saidfused. alkalifcomprises a mixture .of sodium hydroxide and sodium carbonate.

REUBEN F. PFENNIG. CLAUDE R. DAVIS. 

